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Inductor calculator

Inductance

Frequency

Current

Capacitance for resonance

µF

Optional — gives the LC resonant frequency

Series resistance

Optional — gives the L/R time constant

Inductive reactance 62.832 Ω

XL = 2πfL at 1000 Hz

In kilohms 0.06283 kΩ

Voltage across it 62.832 V

Stored energy 5 mJ

LC resonant frequency 1,591.55 Hz

L/R time constant 1 ms

Inductance 10,000 µH

XL = 2πfL · f₀ = 1/2π√(LC)

Inductive reactance is 2πfL. A 10 mH inductor at 1 kHz presents 62.8 ohms, rising in proportion to frequency. With a 1 µF capacitor it resonates at 1,592 Hz, and carrying one amp it stores 5 mJ.

How to use an inductor calculator

1 Enter the inductance in millihenries and the frequency of interest.

2 Read the reactance, which is the AC opposition it presents.

3 Add a capacitance to see the LC resonant frequency.

4 Add a series resistance for the L/R time constant.

Inductors are the mirror of capacitors and the intuition follows from that. A capacitor opposes changes in voltage and passes high frequencies; an inductor opposes changes in current and blocks them. Reactance rises with frequency rather than falling, which is why an inductor makes a good series filter against switching noise and a poor one against mains hum. The stored-energy figure is the one that bites in switching supplies: interrupting an inductor carrying current forces that energy somewhere, and if there is no flyback path it appears as a voltage spike large enough to destroy whatever switched it.

Questions

What is inductive reactance? −

XL = 2πfL, the AC opposition an inductor presents. It rises in proportion to frequency, unlike capacitive reactance which falls.

What is the LC resonant frequency? +

How much energy does an inductor store? +

Why do I need a flyback diode? +

What is the L/R time constant? +

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